1. Field of the Invention
The invention relates to a vehicle control system. In particular, the invention relates to a vehicle control system, in which an electric rotary machine can be cooled with an electric coolant pump.
2. Description of Related Art
For a vehicle with an engine and an electric rotary machine, an oil pump referred to as an electric oil pump or an electrically-driven oil pump is employed as well as a mechanical oil pump, which is driven by the engine, to cool the electric rotary machine, an automatic transmission, or similar component. The electric oil pump and the electrically-driven oil pump are driven with a battery or similar member even when an engine stops.
For example, Japanese Patent Application Publication No. 2011-106296 (JP 2011-106296 A) discloses a vehicle that includes a mechanical oil pump and an electric oil pump and controls automatic stop of the engine according to a driving state of the electric oil pump. Here, the following is disclosed. In the case where the actual rotation speed of a motor of the electric oil pump exceeds a predetermined upper limit value or falls below a predetermined lower limit value, it is determined that a required hydraulic pressure cannot be supplied by the electric oil pump during the automatic stop of the engine and then the automatic stop of the engine is inhibited.
Additionally, Japanese Patent Application Publication No. 2009-228754 (JP 2009-228754 A) discloses a control unit that supplies a hydraulic pressure to a hydraulic mechanism by controlling either an engine-driven mechanical oil pump or a battery-driven electric oil pump. This description also discloses that a degree of deterioration of these oil pumps is determined based on a difference between the target discharge amount and the actual discharge amount of each oil pump, and a driving time ratio of these oil pumps is changed according to this difference, for example.
Japanese Patent Application Publication No. 2002-155865 (JP 2002-155865 A) points out the following. In the case where an electric oil pump is provided together with a mechanical oil pump directly coupled to a crankshaft of an engine, driving only the electric oil pump over long period accelerates its deterioration. This description also discloses that the operation period of the electric oil pump is obtained based on detection signals of a rotation speed sensor of the engine and a vehicle speed sensor, and when the operation period exceeds a predetermined permissible operating period, the engine is started to supply a hydraulic pressure by the mechanical oil pump.
Since the mechanical oil pump is driven by the engine with a sufficient driving force; therefore, influence on fuel consumption is little. However, when the engine stops, the mechanical oil pump cannot cool the electric rotary machine or similar component. Meanwhile, since the electric oil pump is battery-driven, the electric rotary machine or similar component can be cooled regardless of whether the engine is stopped or not. However, the electric oil pump consumes electric power. This reduces economic efficiency of the electric power. Accordingly, operation of the electric oil pump improves performance in cooling the electric rotary machine or similar component while the economic efficiency of the electric power is degraded.
In the running of the vehicle, extending a running distance may be desired by giving importance to the economic efficiency of fuel and the electric power. Meanwhile, increasing an output of a power unit may be desired at the cost of the economic efficiency of the fuel and the electric power. As a condition for operating the electric oil pump of the related art, for example, the electric oil pump starts operating when temperature of a coolant becomes equal to or higher than a predetermined temperature. However, this is not enough to meet economic efficiency, output performance, or other features regarding the running of the vehicle.